External corner lighting is desirable so that a light mounted on a corner or wall can illuminate evenly, typically in the 270.degree. arc around an exterior right angled corner, or the 180.degree. arc around a wall. Another requirement is that the light generating lamp, bulb or tube be easily changeable. This is most easily done by having the canister removable from the corner, otherwise the canister must be taken apart in place, which is generally inconvenient. By having mounting brackets attached around the corner or to the wall and detachably mounting the canister thereon, the canister is made removable. A vertical groove enables the canister to fit the corner more snugly and thus reduces any play caused by wind and weather. Hooks mounted within the canister grooves engage gaps formed between corner and mounting brackets. The close symmetrical mounting of the canister on the corner provides photometrically even lighting from the light or luminaire. Similarly clips mounted on the canister can engage bars mounted on the wall, or bars on the canister may engage clips on the wall, again the canister is closely and symmetrically mounted on the wall providing photometrically even lighting. Equally it may be desirable to direct the light only or chiefly in a specific chosen direction so as to illuminate a specific sector or zone. There is thus a need for the reflector means within the canister to be adjustable.